Preparation And Properties Of Lead-free Metal Halide Based Broadband Long-wavelength-emitting Materials

Broadband long-wavelength light source plays an increasingly important role in food detection,health monitoring,plant growth and night vision.Design and development of new broadband long-wavelength luminescent materials is the key to current research.Thanks to the rapid development of white-LED technology in recent years,the technology of LED chips is becoming mature.The chips are also gradually moving toward miniaturization,such as the emerging Mini-LED and Mirco-LED chips.Due to the low luminous efficiency and narrow emission spectrum of broadband long-wavelength luminescent materials,this paper chooses lead-free metal halide as the host to investigate the origin of self-trapped exciton luminescence（STE）in lead-free metal halides and enhancing its luminescence performance through optimization.The main research contents are as follows:1.All-inorganic double perovskite Cs₂Ag Bi Cl₆ single crystal with three-dimensional structure was prepared by solvothermal method,which realized high efficiency wideband near-infrared emission by alloying Na⁺ion.Experiments and density functional theory（DFT）calculations show that near-infrared emission is derived from intrinsic STE emission,which can be enhanced by weakening the strong coupling between electrons and phonons.As a near-infrared（NIR）luminescent material,Cs₂Ag_0.05Na_0.95Bi Cl₆ single crystal has 51%high luminescent quantum efficiency（PLQY）,270 nm FWHM and excellent stability.NIR-LED based on single crystal has potential application in spectrum detection and night vision.These results indicate that bismuth halide perovskite is an important candidate for broadband NIR luminescent materials and provides a new application direction for luminescent metal halides.2.Three-dimensional inorganic double perovskite Cs₂Na In Cl₆ powder was prepared by solvothermal method,and the extrinsic STE emission was achieved by doping Te⁴⁺ions.Experimental and theoretical calculations show that the emission origins from the STE state introduced by doping Te⁴⁺ions.The optimum performance of Cs₂Na In Cl₆:10%Te powder shows a broad red emission peaking at 643 nm and a FWHM of 180 nm under the excitation of 440 nm,and has good stability.The lower doping amount due to the heterovalent doping and the difficulty in achieving local lattice distortion in the three-dimensional structure of octahedron may be the reason for the weaker STE emission induced by the doped ions.3.Zero-dimensional all-inorganic perovskite-like Cs₂Zn Br₄ powder was prepared by compound precipitation method,and the extrinsic STE emission was achieved by doping Sn²⁺ions.Experiments and theoretical calculations show that the emission is derived from the impurity STE state introduced by doped Sn²⁺ions.The Cs₂Zn Br₄:12.5%Sn powder with the best performance exhibits a broad band NIR emission with the emission peak at 698 nm under the excitation of 320 nm near-ultraviolet light,the FWHM is 177 nm,the quantum efficiency is 41.4%,and has good stability.Powder based NIR-LED has potential applications in the field of night vision.This work provides an effective strategy for developing accessible,environmentally friendly and efficient NIR-emitting all-inorganic metal halides.